[LUCENE-502] TermScorer caches values unnecessarily

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 1.9
• Fix Version/s: 4.0-ALPHA
• Component/s: core/search
• Assignee: Unassigned
• Reporter: Steven Tamm
• Created: 01/Mar/06 11:32
• Updated: 28/Aug/22 11:25
• Resolved: 15/Jul/11 03:00

Description

TermScorer aggressively caches the doc and freq of 32 documents at a time for each term scored. When querying for a lot of terms, this causes a lot of garbage to be created that's unnecessary. The SegmentTermDocs from which it retrieves its information doesn't have any optimizations for bulk loading, and it's unnecessary.

In addition, it has a SCORE_CACHE, that's of limited benefit. It's caching the result of a sqrt that should be placed in DefaultSimilarity, and if you're only scoring a few documents that contain those terms, there's no need to precalculate the SQRT, especially on modern VMs.

Enclosed is a patch that replaces TermScorer with a version that does not cache the docs or feqs. In the case of a lot of queries, that saves 196 bytes/term, the unnecessary disk IO, and extra SQRTs which adds up.